This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        CA carrier aggregation        CC component carrier        CIF carrier indication field        CQI channel quality indicator        CSI channel state information (includes CQI, PMI and RI)        DL downlink (eNB to UE)        eNB EUTRAN Node B (evolved Node B/base station)        E-UTRAN evolved UTRAN (LTE)        LTE long term evolution        MAC medium access control        PDCCH physical downlink control channel        PDSCH physical downlink shared channel        PMI precoding matrix indicator        PUCCH physical uplink control channel        PUSCH physical uplink shared channel        RI rank indicator, UEs recommendation for the number of layers to be used in spatial multiplexing        RRC radio resource control        UE user equipment        UL uplink (UE to eNB)        UTRAN universal terrestrial radio access network        
In the communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or E-UTRA), the LTE Release 8 is completed, the LTE Release 9 is being standardized, and the LTE Release 10 is currently under development within the 3GPP. In LTE the downlink access technique is orthogonal frequency multiple division access OFDMA, and the uplink access technique is single carrier, frequency division multiple access SC-FDMA. These access techniques are expected to continue in LTE Release 10.
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, V8.6.0 (2008-09), and shows the overall architecture of the E-UTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an evolved packet core, more specifically to a MME and to a Serving Gateway. The S1 interface supports a many to many relationship between MMEs/Serving Gateways and the eNBs.
Of particular interest herein are the further releases of 3GPP LTE targeted towards future international mobile telecommunications (IMT)-advanced systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). LTE-A is directed toward extending and optimizing the 3GPP LTE Release 8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Release 10 which is to be backward compatible with LTE Release 8 and to include bandwidth extensions beyond 20 MHz, among others. For an overview see for example 3GPP TR 36.913 v9.0.0 (2009-12) Requirements for further advancements for Evolved Universal Terrestrial Radio Access (E-UTRA) (LTE_Advanced) (Release 9).
The bandwidth extension in LTE Release 10 is to be done via carrier aggregation (CA), in which several component carriers, at least one of which is Release 8 compatible, are aggregated together to form a system bandwidth. This is shown by example at FIG. 2 in which there are five Release 8 compatible CCs aggregated to form one larger LTE Release 10 bandwidth. Existing Release 8 terminals can receive and/or transmit on at least one of the CCs for backward compatibility, while future LTE-A terminals could potentially receive/transmit on multiple CCs at the same time to give the eNB greater scheduling flexibility while increasing data throughput.
In LTE Release 8/9, there is no CA and so there is no ambiguity as to which PDSCH/PUSCH is referred to by a particular PDCCH. LTE-Advanced, so-called “cross-CC scheduling” has been supported via carrier indicator field (CIF), which means the PDCCH could be used to indicate PDSCH/PUSCH resources sent on other CCs indicated by CIF. From the PDCCH transmission perspective this is useful for uneven traffic loads among multiple carriers, and/or in a heterogeneous environment where cross-scheduling is used to schedule using the CC which has less interference.
Specifically, in LTE Release 8/9, the periodic CQI/PMI/RI report is configured by higher layers and transmitted on the PUCCH. The aperiodic CQI/PMI report is triggered by a 1-bit CQI-request in DCI format 0 or by a Random Access Response Grant transmitted on the PUSCH. It may be advantageous to configure periodic CQI/PMI reporting independently for each CC in the CA arrangement of LTE Release 10, such as with similar parameters as used in LTE Release 8/9 (for example; periodicity, subframe offset, resource allocation, reporting mode). This is much less practical for aperiodic reports since by their nature they are not repeating, and so extending the LTE Release 8/9 rules to each CC in a CA system would impose a high control signaling overhead.
In LTE-Advanced, multiple DL CCs may be configured/activated for one UE. Among these DL CCs, there may be dynamically requested aperiodic CQI/PMI reports on one or multiple DL CCs. In such case, 1-bit CQI-request is obviously insufficient to trigger aperiodic CQI/PMI/RI report for one or multiple selected CCs. In such a case, for aperiodic CQI/PMI/RI report the UE needs to know which DL CC(s) eNB needs aperiodic CQI/PMI/RI report, and also which UL CC is used to convey aperiodic CQI/PMI/RI report. The one-bit signaling mechanism in LTE Release 8/9 is insufficient to signal this more expansive but necessary information.
There have been some attempts to design a system for LTE Release 10 to trigger aperiodic CQI/PMI reporting for a specific DL CC. One approach is to extend the bit-length of the CQI-request field. The inventors see this as less than optimal because in order to avoid increased the UE's blind decoding efforts, additional padding bits will be introduced (for example, to the DCI format 1A), which means additional payload waste. This approach is described generally at International Patent Application no. PCT/EP2010/053919 (filed Mar. 25, 2010).
Another approach is to re-use some bits in DCI format 0 to carry the additional information needed in the case of multiple DL CCs. These “enhanced CQI-request bits” may be for example padding bits, or CIF, or RA bits. But in fact these bits are not always unused and so to make them always available for such enhanced CQI request bits would appear to impose scheduling restraints on the eNB, and 3GPP LTE aims to maximize network scheduling flexibility as a means to most efficiently deploy radio resources. This approach is also described at the above-cited PCT/EP2010/053919.
A third approach, outlined in document R1-101262 entitled “Aperiodic CQI Reporting for Carrier Aggregation (3GPP TSG-RAN WG1 Meeting 60 (22-26 Feb. 2010, San Francisco, Calif. USA), is to use the one-bit CQI request of LTE Release 8/9 to trigger in LTE Release 10 an aperiodic report for all DL CCs. This is inefficient from an UL signaling overhead point of view since the eNB will not always needs aperiodic CQI/PMI/RI reports for ALL configured/activated DL CCs.
International Patent Application no. PCT/EP2009/050039 (filed Jan. 5, 2009) proposes identifying the best CC and only reporting a frequency selective CQI for that particular CC, plus potentially reporting wideband for other CCs. A publication entitled “Downlink PDCCH Signaling and CQI Measurement for LTE-A Bandwidth Extension” (disclosure number IPCOM000178173DE dated Feb. 13, 2009, seen at http//ip.com/IPCOM/000178173) proposes letting the CC being CQI-reported hop depending on a modulo operation of the system frame number (SFN) and the UE ID.